Engineering of the catalytic site of xylose isomerase to enhance bioconversion of a non-preferential substrate

Mutation in active site would either completely eliminate enzyme activity or may result in an active site with altered substrate-binding properties. The enzyme xylose isomerase (XI) is sterospecific for the α-pyranose and α-fructofuranose anomers and metal ions (M1 and M2) play a pivotal role in the catalytic action of this enzyme. Mutations were created at the M2 site of XI of Thermus thermophilus by replacing D254 and D256 with arginine. Mutants D254R and a double mutant (D254R/D256R) showed complete loss of activity while D256R showed an increase in the specificity on D-lyxose, L-arabinose and D-mannose which are non-preferential substrates for XI. Both wild type (WT) and D256R showed higher activity at pH 7.0 and 85°C with an increase in metal requirement. The catalytic efficiency Kcat/Km (S(-1) mM(-1)) of D256R for D-lyxose, L-arabinose and D-mannose were 0.17, 0.09 and 0.15 which are higher than WT XI of T.thermophilus. The altered catalytic activity for D256R could be explained by the possible role of arginine in catalytic reaction or the changes in a substrate orientation site. However, both the theories are only assumptions and have to be addressed with crystal study of D256R.     

Multifunctional Dy(Ⅲ) doped di-calcium silicate array for boosting display and forensic applications

Latent fingerprints(LFPs) are the major physical evidences for the identification of individuals during crime spot investigation. Till date, numerous methods were followed to visualize LFPs. However, simple,accurate, and cost-effective method has wide scope in advanced forensic field. In our work, Ca_2 SiO_4:Dy~(3+)nanopowders(NPs) were fabricated via solution combustion route. The optimized sample was employed for the visualization of overlapped LFPs by the cost effective powder dusting method. The obtained results reveals the complete three levels of ridge characteristics with high sensitivity, reproducibility,selectivity, and reliability on various complex surfaces. The photoluminescence(PL) spectra consist of intense peaks at ～ 480 and 574 nm owing to ~4 F_(9/2) →~6 H_(15/2) and ~4 F_(9/2)→~6 H_(13/2) 4 f transitions of Dy3+ ions,respectively. The photometric properties confirm that the samples exhibit intense white emission with high color purity. Therefore, the prepared NPs could be a definitive choice as an advanced luminescent NPs for forensic, solid state lighting and portable FED devices.     

Degumming rice bran oil using phospholipase‐A1

The efficacy of enzymatic degumming was assessed using the third generation phospholipase‐A₁, Lecitase®‐Ultra (EC 3.1.1.3) from Thermomyces lanuginosa/Fusarium oxysporum with different qualities of crude rice bran oil. The phosphorus content in the oil reduced to ～10 mg/kg from an initial level of 390 mg/kg after 2 h of incubation period at 50°C. However, in the solvent‐phase degumming, there was practically no phospholipid reduction at lower water content (2%) due to the poor contact between the highly nonpolar solvent and the aqueous phase (citric acid, NaOH, and enzyme solutions). Increasing the water content to 20% reduced the phosphorus level in the degummed‐oil to 71 mg/kg but did not match the performance of oil‐phase degumming. The degumming efficiency of Lecitase®‐Ultra was effective in oil‐phase and suitable for practical application. Solvent‐phase enzymatic degumming offers more benefits but needs greater efforts to overcome the challenges.     

Amyloglucosidase-catalyzed synthesis of n-octyl-d-glucoside—analysis using response surface methodology

Amyloglucosidase (3.2.1.3)-catalyzed synthesis of n-octyl-d-glucoside was optimized using response surface methodology. A central composite rotatable design involving 32 experiments of five variables at five levels was employed to study the glucosylation reaction. Among the variables studied, namely, n-octanol (15–75 MEq to d-glucose), enzyme (20–100 mg ), pH (4.0–8.0), buffer volume (0.2–1.0 ml) and temperature (30–70°C), amyloglucosidase concentration, pH and temperature were found to be significant. Experimental data fitted the second-order polynomial equation well, as indicated by an R² value of 0.895. Validation experiments carried out under predicted conditions showed good correspondence between experimental and predicted yields. Various surface plots were generated to describe the relationship between operating variables and the conversion yields. The highest yield of 53.5% predicted at optimum conditions of 75 Eq n-octanol, 20 mg amyloglucosidase, 0.2 ml, pH 7.8 buffer at 50 °C showed good correspondence to the experimental yield of 53.8% under these conditions.     

Healthy aspect of low‐cholesterol ghee on modulation of lipid profile of rats

Low‐cholesterol ghee (LCG) feeding did not show any significant increase in total plasma cholesterol level from day 0 (56.8 ± 6.8 mg/dL) to day 90 (59.5 ± 0.8 mg/dL). Plasma HDL cholesterol (HDL) levels increased by 59.9%, whereas LDL cholesterol (LDL) showed a reduction of 74.8%. Total plasma triacylglycerol (mg/dL) did not show any significant change within or between groups. Relative contribution of lipoprotein fraction HDL was 69% vs 47% in control. Atherogenic Index was low (0.47 ± 0.05) vs 1.03 ± 0.2 in the control. Deposition of cholesterol in arteries and liver was also less (0.423 mg/g tissue) than in control (0.648 mg/g tissue). Feeding LCG improved the lipid profile of rats.     

Novel topologies for DC-DC converter with PWM control

Two topologies for the buck converter are presented. The first converter consists of two active switches whereas the second converter, derived from the parent twoswitch converter, consists of only one active switch. The main feature of this new converter is the ability to operate at a constant switching frequency using a simple PWM control. The design of the gate circuit is simplified as there is only one switch. The converter has a good efficiency, as is proved by the experimental results. The operation of the parent two-switch converter, from which the new single-switch converter is derived, is also presented to gain insight into the design of the new converter.     

Increased dietary arachidonic acid enhances the synthesis of vasoactive eicosanoids in humans

Data on the effect of dietary arachidonic acid (AA) (20∶4n-6) on the synthesis of thromboxane and prostacyclin (PGI₂) in humans are lacking. We measured the effect of 1.5 g/d (ca. 0.5 en%) of 20∶4n-6 added isocalorically to a stabilization (low-AA) diet on the excretion of 11-dehydrothromboxane B₂ (11-DTXB₂) and 2,3-dinor-6-oxo-PGF_1α (PGI₂-M). In a crossover design, 10 healthy men, living in a metabolic unit, were fed a diet (low-AA) containing 210 mg/d of 20∶4n-6 for 65 d and an identical diet (high-AA) that contained 1.5 g/d of additional 20∶4n-6 for 50 d. Three-day urine pools were collected at the end of each dietary period and analyzed for eicosanoids by gas chromatography-electron capture negative ion-tandem mass spectrometry. Mean excretion of 11-dehydrothromboxane B₂ was 515±76, 493±154, and 696±144 ng/d (SD; n=10) during the acclimation (15 d) low-AA diet and high-AA diet periods, respectively (41% increase from low-AA to high-AA diet, P=0.0037); mean excretion of PGI₂-M was 125±40, 151±36, and 192±55 ng/d (SD; n=10) during acclimation (15 d) low-AA and high-AA diets, respectively (27% increase from low-AA to high-AA diets; P=0.0143). Thus, both the metabolites of thromboxane and PGI₂ increase on the high-AA diet. Furthermore, both indicated changes in metabolite excretion may be associated with measurable effects on several physiologically significant cellular functions, such as platelet aggregation in vivo and inflammation in response to immune challenges.     

Superconductivity in dense Mg11-xMxB2 (M = Zr, Nb, Mo; x = 0.05) materials sintered under pressure

Dense compacts of superconducting MgB₂ material have been produced by sintering under 3 GPa pressure and 900°C using a cubic anvil apparatus. The starting material was produced by the powder in tube (PIT) method at low pressure and in argon atmosphere. The effect of substitution of Mg sites with non-magnetic 4d-transition metals (Zr, Nb, Mo) on the superconducting transition temperature (T inc) has been studied by resistivity and susceptibility measurements. The results indicate that there is a small gradual reduction in the transition temperature as we move from Zr to Mo.